This is a continuing study of the follow-up of an aging population for residents in a County Home and Hospital. The initial sera was collected in 1970 and the subsequent collections were made in 1974 and 1975. The follow-up of the patients is conducted by examination of charts, personal interviews and examinations, and examination of autopsy and county death records. Immunologic features that have been measured are levels of IgG, IgA, IgD and IgE, C3 and C4 complement factors, rheumatoid factor by latex titer tests, thyroid antibody by sheep cell agglutination, thyroid microsomal antibody and hemagglutination tests for antibodies to E. coli and Shigella. The population is extensive and consists of 357 individuals ranging in age from 31 to 100 with the majority of patients 60 and above (282). Formulation of normal values for the aging population will be established by this study. In addition, the study will establish relationships of antibody levels and presence of different types of antibodies to types of death and disease present in the patients.